Cursor line and map generator



N0V 25, 1958 D. J. GREEN ETAL 2,862,202

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FEEQUENC'V Nov. 25, 1958 D. J. GREEN ET AL 2,862,202

cuRsoR LINE AND NAP GENERATOR Filed April 2s, 1951 e sheets-sheet 2 IN V EN TORS m, @www @nM/ana 5.1775469,

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cuasoa LINE AND MAP GENERATOR Nov. z5, 195s Filed April 25, 1951 www@ f OO- D. J. GREEN ETAL 2,862,202

' cURsoR LINE AND MAP GENERATOR Nov. 25, 1958 Filed April 2s, 1951 6 Sheets-Sheet 4 @NGE D. J. GREEN ET AL 2,862,202

f 6 Sheets-Sheet 5 CURSOR LINE AND MAP GENERATOR Nov. 25, 1958 Filed April 23, 1951 Nov. 25,v 1958 Filed April 2s, 1951 E .mw mwk SRSWN WI m I/QO. .Q n N nited States Patent 2,862,202 Patented Nov. 25, f9.5@

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CURSUR LNE AND MA1 'GENERATR- David l. Green, Pacific Palisades, Raymond B. Tasker,

Sepulveda, and'Bur-ton Cutler, Los Angelas, Calif., assignors toGilllan Bros., Inc., Los Angeles, Calif., a corporation of California Application April 23, 1951; Serial No. 222,511 27 claims, (Ct 34a- 11) The present invention relates to an improved indicating system in which-a predetermined path, either in the horizontal plane or in the vertical plane, which aircraft should take is produced electronically on a cathode ray tube, and relates more generally to improvements in radar indicating systems such as those heretofore used in ground controlled approach (G. C. A.) radar systems.

ln prior art systems, in the precision section of G. C. A. equipment, the position of an aircraft while ying in the approach zone to a landing held is portrayed in two distinct displays simultaneously on a cathode. ray tube, onerof such displays being in terms of elevation and range' and the other display being in terms of azimuth and range. Such displays allow a determination of the position ofi the aircraft in three dimensions.` lnV such indicatingV systems it was heretofore customary to indicate physically on each of such displays the optimumzp'athlwhich thev aircraft should take in effecting a safe landing. Fori that purpose, overlays with'predeterrnined glidepaths (with' reference to the elevation displaylor runway paths (with reference'to the azimuth display) were placed on the viewing face. of the cathode ray tube, in the `manner described more fully in the copending application ofHomer G. Tasker et al.Serial No; 776,702, lile'd September 29, 1946, now Patent No. 2,649,581, and assigned to-thel same assignee as the present inventioni rl`he preseutinvention' contemplates the production of displays ofthis character in which the safe glidepath, in the caseof the elevationy versus range display,Y and the runway` path inV the'lazimuth versus range display, are both produced electronically for purposes of accuracy, and. further toavoid. the necessity of the `use `ofi-thesey overlays,.and further to avoid: drift resultinglin other elements of the electronic. ecpiipment,` auch asv in the' sweep amplier andthe like. i

Itis therefore a general object ofthe present inventionv to provide -apparatusxand techniques whereby theaforementioned results may be obtained electronically.-

In some respects the invention has broader'aspects and may be used for other purposes in which any otherdesired line onta display or portion of a line may be produced electronically or control effects produced in terms'of time delay and antenna beam angle voltage.

Another object of the present invention is to provide" improved apparatus for this purpose using principles embodied in analogue computers.

Stated in other words, an additional object of the present- 2 reference to the following description takenin connection with the accompanying drawings in which:

Figure l shows two displays produced on the viewing face of the cathode ray tube in accordance with features of the present invention;

Figures 2A, 2B and 2Cshow, in schematic form, portions ofthe apparatus used in producing the'display shown in Figure l, it being noted-that the terminals which are to be connected in these Figures 2A, 2B and 2C are represented by the same notations, and when thus connected Figures 2A, 2B and 2C comprise Figurev 2;

Figure 3 is a three-dimensional representation useful in explaining the problems involved Aand solutions made in accordance with the present-invention;

Figure 4 is helpful in describing the cyclical operation of the antenna scanning mechanism andlassociated 'equipment shown in Figure 2A;

Figure 5 shows, in graphical form, the voltage variations derived in accordance with scanning movement of the azimuth and elevation antennas shown'in Figure 2A as a function of the angularV position ofthe corresponding radiated antenna beam, the portions of these curves shown in full lines being referred to herein as antenna beam angle voltage, and are used in' effecting important control operations in accordance with features of the present invention;

Figure 5A is a schematic representation for' purposes of illustrating th'etime scans of the elevationtblankingV gate, the azimuth blanking gate and the Az-El'relaygate;

Figure 6 is a schematic representation showing the apparatus of Figure 2B in more simplified form;

Figure 7 'is a schematic' circuitdiagrani illustrating a circuit for 'establishingthe electrical 4center off'th cathode ray' tube display;

Figure 8 is a schematic repre'sc n'tatinn of aY modified arrangement using principles ofthe present invention for purposes of display limiting'or clipping invention resides in improved apparatus to simulateV elecl Figures 9 and l() are graphs helpful in understandingthe interrelationship of physical Vand 'electrical quantities and result produced by the apparatus described -herein in producing the=runway` course line when' the radar apparatus is located for left of runway operation;

Figures ll and l2 are graphs likewise helpful in understanding the interrelationship of physical and electrical quantities and result produced by the apparatus described herein in producing the glide path course line, and is further helpful in understanding'the manner in which the runway course line is produced when the radar apparatus is located for right of runway operation.

In general, the apparatus described herein serves to produce the elevation display 10 (Figure l) and azimuth display 11 with the predetermined safe glide path represented bysthe line AB in the elevation display 10, produced electronically as a series of dashes, and to correspondingly produce electronically the -runway line in the azimuth display 11 represented by the-line CD. This is for the general purpose of allowing an observer to track the course of an aircraft appearing as the dots 12,'13 on` the elevation and azimuth displays, respectively, with reference to such corresponding lines AB and CD.

It is noted that these displays 10, 11 are produced by radial cathode ray beam sweeps originating from the ad-y justed electrical centers O1, O2 of the cathode beam deflecting system. The series of vertically aligned lines 14,V 15, 16, 17, 18 and 19 in both displays 10, 11 represent range lines, i. e., the locus of points of constant distance from the centers O1 and O2, as the case may be. The range line 14 passes through the aircraft touchdown point A on the elevation display, and of course through'theY small rectangular tab 20 which may be placed on the faceof the cathode ray tube to indicate the position of the' aircraft landing strip. The line 14 in displays 10 and 11 thus represents zero distance from touchdown. The lines 15, 16, 17, 18-and 19 represent, respectively, distances two miles, four miles, six miles, eight miles and ten miles from the corresponding touchdown point in the azimuth and elevation displays 11, 10.

It will be observed that the elevation display and azimuth display 11 are irregular in shape, and such irregularities in the displays are produced by pattern limiting or clipping so as to allow more eicient use of the viewing surface of the tube and to allow the most imsortant portions of the displays 10, 11 to lie closer to ich other. For purposes of reference, the elevation disay comprises the area defined by O1, F, G, H, J, K, O1. yLnilarly, for purposes of reference, the azimuth display ,1 is conned in the area defined by O2, L, M, N, P, O2. The pair of radially extending lines 22, 23 in the elevation display are well known so-called V-follower lines, produced in accordance with conventional means, and serve to indicate the area scanned by the azimuth antenna. Similarly, the pair of radially extending V-follower lines 24 and 25 in the azimuth display 11 indicates the area scanned by the elevation antenna.

As indicated above, the present invention concerns itself particularly with the electronic production of the' glide path line AB and runway line CD. However, before entering into a detailed discussion of the apparatus and method used in producing such lines AB and CD, the apparatus for producing the displays 10 and 11 is first described in connection with Figures 2A, 2B and 2C which, when interconnected as indicated thereon, serves as Figure 2.

Pattern producing means In Figure 2A the synchronizer 31 serves to generate timing pulses which are used to time the operation of pulses applied to the transmitter 34 to initiate its operation. The transmitter stage 34, pulsed at a constant repetition rate of, for example, 2,000 pulses per second, consists of,'for example, a magnetron oscillator with a characteristic frequency of about 10,000 megacycles. The output of this transmitter stage 34 is transferred to either the elevation (El) antenna 37 or azimuth (Az) antenna 38,' depending upon the position of the motor driven interrupter or radio frequency switch 36, The transmit-receive (T-R) switch 35 prevents power from theV transmittter 34 from being applied directly to the receiver 39. This transmit-receive switch 35, as is well known in the art, allows low intensity signals such as a train of resulting echo signals received on the antennas 37, 38 to be transferred to the input terminals of the receiver 39.

This diversion of energy from the transmitter 34 to the antennas 37, 38, accomplished by operation of switch 36, occurs at a rate of approximately 2 per second, so that in efect the combined antennas obtain 4 looks per second of the space scanned. VThe resulting antenna beams are caused to move angularly, i. e., to scan upon rotation of the shaft 26. The switch 36 is rotated twice per second, and while energy is being transmitted to one of the antennas 37, 38, the resulting electromagnetic beam projected into space is caused to scan such space. The means whereby such scanning movement of the projected electromagnetic beam is obtained may be of the type described in the copending application of Karl A. Allebach, Serial No. 49,910, led September 18, 1948, nowV Patent No. 2,596,113, for Bridge Type Precision Antenna Structure, which depends for its operation on the use of a variable wave guide type of antenna. This particular means, per se, forms no part of the present invention, and, so far as the aspects of the present invention are concerned, the antenna scanning beam may be produced by moving the entire antenna through a relatively small arc of Va circle. Actually, in fact, the azimuth antennabeam may scan rst in one direction and then in theother,

4 4 waiting after each scan while the elevation beam completes a scan in elevation.

While in any position during the part of the cycle in which the R. F. switch 36 allows the flow of energy to the elevation antenna 37, the elevation antenna beam is electrically scanned in elevation. The angular position of the elevation antenna beam is measured by means of a variable capacitor 27, one plate of which is attached to the beam scanner of elevation antenna 37 and varied in accordance therewith, such capacitor 27 comprising one part of a capacitative potentiometer contained in the angle coupling unit 28, which may be of the type described and claimed in the copending patent application of George B. Crane, Serial No. 212,114, filed February 2l, 1951, now U. S. Patent No. 2,650,358. The angle coupling unit 28 thus used with angle capacitor 27 is useful in developing the elevation beam angle voltage represented as 27A in Figure 5. Similarly, the angle in azimuth of the azimuth antenna beam is measured by the angle capacitor 29 in azimuth angle coupling unit 29A, operating synchronously with the scanner of the azimuth antenna 37. Such variation in azimuth angle voltage as a function of the particular angular position of the antenna beam is represented by the cyclically varying voltage 29B shown in Figure 5. It is observed that these voltage variations 27A and 29B have portions thereof shown in heavy lines, and it is these portions which are used to effect control operations, and which are selected upon alternate closure of the isolating switches 29A and 28A, respectively. These switches 29A and 28A are operated in synchronism with the shaft 26 by mechanical connections indicated in dotted lines.

Figure 5 also shows, for purposes of reference, inverted useful elevation beam angle voltage as represented by the oblique lines 27B.

Also coupled to the scanner of the elevation antenna 37 is the elevation unblanking or cathode beam intensifying switch 45, which has one of its terminals connected to the continuous voltage source 46, for purposes of developing an elevation unblanking voltage or gate so timed that its positive value corresponds to the time of effective scanning of the elevation antenna beam. The unblanking or beam intensifying switch47 is similarly coupled to the scanner of azimuth antenna 37, with one of its terminals connected to the continuous voltage source 48 for purposes of developing unblanking or intensifying voltages so timed that the positive portions of such voltage correspond to the time, of effective scanning of the azimuth antenna beam. Relay switch 49 operates at substantially the same time as switch 47, and synchronously therewith serves to generate the so-called Az-El relay voltage or gate (Figure 5A) which is so timed that its positive portion begins at a time just prior to the beginning of the azimuth unblanking voltage and just after the end of elevation unblanking voltage, and which ends at a time just after the ending of the azimuth unblanking voltage and just prior to the beginning of the elevation unblanking voltage, all as seen in Figure 5A.

Figure 4 shows a schematic diagram of the time relations involved in a scanning cycle, which typically occupies a time in the order of one second. Forward progress of time is represented by clockwise motion about this diagram. The central circular region of Figure 4, marked N, shows the time schedule of the scanning operations of the two systems, opposite quadrants representing cornplete scans by the same system but carried out in opposite directions. The shaded areas (each comprising roughly 10 of the complete 360 cycle) represent the periods during which the transmitter 34 is switchedby the switch 36 in Figure 2A from one antenna to -thc other. Unshaded areas of region N represent the time periods during which one or the other of the antennas is in use, sending out radio frequency pulses and receiving reflected echo signals from objects within the field of coverage of the beam. Shaded areas indicate inactive .Periods .during-.which .switchingtakes place, ,both antennas being Yimornentfarily isolated from, 1the ,transmitter Yand receive'r.

The inner annular region M of "Figure `4 represents the timeschedule of the related azimuth and elevation displays, subject, however, -to pattern clipping described later, and corresponds to the. cyclical variations. of azimuth andelevation voltages.. representedin FigurefSAand applied to the intensitycontrol electrode, i. e., :grid 51A, of the cathode ray. tube 5.1, `using, theswitches 5451 and 47 for that purpose. the cycle'duringjwhich this grid voltage isrfapplied, shaded area periods when this grid rvoltage is cut oi, rnaking the tube inoperative, i. e., dark, even in -the presence of video signals and sweep intensifying voltages applied respectively to the'cathod'eSlB and grid 51A in the man- -ner hdescribed later.

Theouter 'annular region of Figure 4, `marked L, shows :the time'schedule; ofV Currentsfthrough the .various coils `of a number ofV so-called Az-El, switching relays :for effecting time sharing. The relay actuating .current is obtained by the switch 49roperating in synchronism with the mechanism producingazimuth antenna beam scanning.

Moreydpecically, in'FigureLZA, `the wave guide transmission line 53 leads from the 'transmitter` 34 and receiving system 35, 39. A T-.joint 54 divides this transmission line into .two branches 55 and 56, leading through switch :assembly 3.6 to the. azimuth land elevation assemblies 38, 37, respectively. VThesebranches have suitably placed Vshutterslots which receive the rotating-shutters 57 and A58, respectively. These are mounted on the common drive shaft` 26, .driven by thel motor 59, and have two .blades each Varranged in opposite fashion, so that when fone antenna transmission branch isV opened, the other will be blocked by its shutter. The shutter blades 57, 58 cover angles of approximately V100, leaving openingsof 80 as required by region N of Figure 4.

The samedrive shaft 28 operates the two antenna beam scanning mechanisms, represented by the dotted lines 60, 61, and assumed to 'be of the construction in the above mentioned All ebach application and built into the antenna assemblies. In the showing of Figure 2A, the eccentric cams 62, 63on shaft 26 operate the beam scanning -mechanism Since each of the cams 62, 63 has one lobe, while its associated shutter 57 or 58 has two lobes, one opening in the shutter will find the antenna scanning in one direction, the other in the other direction. The azimuth and elevation blanking switches 45 and 47 are shown schematically in Figure 2A as cam actuated, being operated by the two-lobed cam 64, for purposes of establishing the unblanking or intensifying voltages represented in Figure 5A.

The Az-El relay switch 49 is 4operated by the cam 65 on shaft 26 vto control ycurrent to the circuit switching relays, the function of which is described hereinafter.

The radar echo signal, when lreceived at the elevation antenna 37 or the azimuth antenna 38, is fed back through the R. F. switch 36 and passed through the tune-receive switch 35 into the receiver 39. Receiver 39 serves to detect the video, .and after the video is .amplified in the video amplifier stage 5th it is applied to an intensity controlling electrode of the cathode ray tube 51 (Figure 2C), i. e., to the grid ltA. Also applied to the grid SlA are range marks which are developed in the range mark generator 52 in accordance with triggers supplied thereto from the synchronizer 31.

The cathode ray tube 51 has a pair of magnetic deflection coils 67, 63, so arranged as to deflect the associated electronbearn substantially parallel to two mutually perpendiculaiaxes, the so-called time base axis which is generally, although not exactly, horizontal as viewed by the operator and as shown in Figure l, and the soacalled expansion axis which is generally vertical, In general, each basic trigger pulse developed in synchronizer 31 (Figure 2A) is made to initiate a current wave yof-saw- Unshaded areas represent parts of -tooth form through the time base deflection coil 67, and a Vcurrent wave of similar form through the associated expan'sion deflection coil 468, the current in each coil expanding approximately linearly with time and then returning rapidly to zero. Instead of a linear variation, this variation may be logarithmic in character, as described in thecopending patent application of Homer G. Tasker et` al., Serial No. 175,168, led July 21, 1950, now Patent No. 2,737,654, and assigned to the same assignee as the present application.

The repetition rate of such sawtooth currents is, of course, the same as .the pulse repetition rate of the transmitted pulses, and occurs during the expectant period of resulting Vecho signals. It will be understood that electrostatic deflection of the cathode ray beam may be used instead of electromagnetic deection, appropriate modications being madein other parts of the equipment.

Such sawtooth currents applied to the deflection coils 67, 63, however, are modulated at a slow rate by currents of m-uch lower periodicity which are produced by voltages, i. e., the beam angle voltages which are produced in ,accordance with the vscanning movement of the antenna beam, and which are shown graphically in heavy lines in Figure v5. Those portions of the voltage indicatedin heavy lines in Figure 5 only are used to modulate the sweep voltages on a time sharing basis.

These voltages, as represented by the curves 27A and 29B, -may vary-from plus two volts at one extreme of the scanning range ,to plus fifty-two volts at the other end. These lparticular antenna beam angle voltages, as mentioned previously, are used in eiect to .modulate the amplitude of the sawtooth voltage waves developed in `the sweep amplifier shown in Figure 2C and applied at a muchhigher repetition rate `to the expansion coil 68, for purposes of obtaining unidirectional or unidimensional magnification in the cathode ray display in accordance Vwith principles set forth in the4 copending patent application of Homer G. Tasker, Serial No. 680,604, tiled July l, 1946,-now abandoned, and assigned to the same assignee as the present application. On the other hand, the amplitude ofthe sawtooth voltage waves Vdeveloped inthe sweep amplifier and` applied to the other quadraturely acting time base coil 67 is likewise modulated to a much smaller degree and in a different manner, for purposes of orientation as'described later.

Thus, the amplitude of the currents supplied to coil 68 is automatically varied in accordance with antenna beamangle voltage, so that the angle which any particular cathode ray beam makes, corresponds, on an expanded scale, to the antenna beam angle.

The tube Slis rendered fully operative for producing visible indications only when suitable intensifying volt-` ages in the for-m shown in Figures 5A and 2C are .applied to its grid 51A, bringing the tube approximately -to cutolf condition. A relatively small additional video signal or range mark signal (or cursor pulse described later) then strengthens the cathode beam, making it momentarily visible on the screen as a dot, the position of which is determined by the currents owing at that particular moment Vin the set of deflection coils 67, 68.

For purposes of developing suitable deflecting currents in the cathode ray deflection coils 67 and 68, and the sweep unblanking or intensifying pulses indicated in Figure 2C, the sweep generating circuit `shown in Figure 2C is supplied with pulses from the synchronizer 31. Such pulses, in the form of triggers, are fed from the synchronizer 3l to the delay multivibrator and blocking oscillator stage 69, the output of which is fed to the sweep generating multivibrator stage 70. The Vstage 70 generates a gating or intensifying pulse which is fed to the second mixer stage 7l to produce the composite wave form 73 shown in Figures 2C and 5A. This wave 73 comprises .pulses ofsweep frequency added to the longer. azimuth and elevation gating voltages developed in the lirst mixer stage 72, such rst mixer stage 72 serving to combine the of the composite wave 73 is required to be present to bring `the cathode tube 51 up to the point of cut-olf during application of sweep currents to the coils 67 and 68. A negative gating voltage is also generated in the stage 70 and fed to the expansion and time base modulator stages 75 and 76, respectively, 4and from them in modulated form through expansion and time base ampliers 77 and '78. The output of amplifiers 77 and 78, in the form of essentially trapczoidal waves of appropriate amplitude are applied to the expansion deflection coil 68 and the time base deflection coil 67, respectively, causing .current pulses of linear sawtooth form in the coils. Expansion and time base centering circuits 79 and 80 are also connected to the detlection coils. The modulator stages 75' .and 76, for purposes of modulation, receive antenna beam angle voltages via switches m and n, respectively, of relay K118i.

With the relay unactuated (as shown) the elevation beam angle voltage appearing on the potentiometer resistance 81 is applied through switch m to the expansion modulator 75; and through potentiometer resistance 82 and inverter 83 and switch n to the time base modulator 76. After completion of the elevation scan, relay K1101 is actuated by switch 49, breaking the elevation beam angle voltage connections just described, and connecting the azimuth beam angle voltage through potentiometer 84 and switch m to the expansion modulator; and through vpotentiometer 85, inverter 86 and switch n to the time base modulator.

The potentiometers 81, 82, 84 andl 85 control the amplitudes of the antenna beam angle Voltage supplied directly to the expansionmodulator 75 and supplied indirectly through the inverter to the time base modulator. Thus, the degree of modulation of sweep current, and

hence the degree of angle expansion of the display, may

be separately regulated for the azimuth display by adjustmentof the potentiometer 84, and for the elevation display by adjustment of potentiometer 81; and the degree of modulation of the time base sweep current, and hence the apparent angle between the range marks and the time base, may be separately` regulated for the azimuth display by adjustment of potentiometer 85, and for the elevation display by adjustment of the potentiometer 82.

The centering circuits 79 and 80 in Figure 2C are individually capable of two separate adjustments, one effective when relay K1102 is actuated (azimuth display) and one when the relay is unactuated (elevation display) to determine the positions of the points O2 and O1, respectively, in Figure 1. Thus, the originsV of azimuth and elevation displays are separately, adjustable, the centering circuits automatically responding to one or other set of adjustments according to the energized condition of relay K1102. A schematic diagram showing centering circuit for expansion deflection coil is shown in Figures 2C and 7.

The deflection coil 68 in Figure 7 is connected between a 70D-volt positive supply and two parallel circuits, one leading to ground through tube VV1116, which is the nal stage of expansion amplifier 77, and the other leading through choke coil L1101 and centering tube V1117 to a 100G-volt positive supply. The rst of these two circuits feeds to deflection coil 68, the periodically varying sweep producing component, while the second circuit provides a relatively constant but adjustable centering current component. The cathode resistor of centering tube 68A is -made up of two parallel connected potentiometers R1158 and R1159, the movable contacts of which are connected respectively to the normally closed and normally open contacts of switch m or relay K1102. A switch arm is connected through grid resistor R1157 to the tube grid. 'I'he grid bias, and hence the centering current through the tube and through `the coil 68 thus depends upon the position of relay switch m being determined by the setting of potentiometer R1159 when relay 1(1102 is actuated Y 8 (azimuth display) and by the setting of potentiometer R1158 when the relay is not actuated (elevation display), YThe two displays are .thereforeseparately adjustable as to their vertical position (expansion component) on the indicator tube Vbymeans of the two potentiometers.

Time base deflection coil 67 is provided with centering circuitry which is identical to that in Figure 7 and functions in a like manner, controlled by switch n of relay kK1102. VIn fact, by appropriate changes of the numerals and lettering, Figure 7 may be considered to illustrate the time base centering circuit., The potentiometers then provide separate adjustments ofV the elevation and azimuth displays with respect to their horizontal positions (time base component).

Pattern limiting or clipping The azimuth and elevation displays 11, 10 in Figure 1 are clipped or limitedV by means which, per se, form no part of the present invention, although two such means for accomplishing such pattern clipping or limiting are s'hown briefly herein. For example, the azimuth display 11 may be clipped `or limited along the line LM and the elevation display 10 clipped or limited along the line KJH by means which are described in detail in the copending patent application of one of the inventors herein, Raymond B. Tasker, Serial No. 212,163, tiled February 2l, 1951, now Patent No. 2,663,868, and assigned to the same assignee as the present application. Such means are included in the sweep limiter 90 shown in Figure 2C the output ofvwhich is applied to the rst anode 51C of the cathode ray tube 51 in the form of a negative blanking voltage 91, the position of which Vis shiftable along the time axis in a degree depending upon the particular .value of azimuth or'elevation beam angle voltage, as the case may be. For this purpose, the sweep limiter 90 is ,supplied `with delayed synchronizing pulses from the delay multivibrator 69, and is supplied with azimuth and elevation beam angle voltage, and likewise is supplied with map relay gating voltages, all in accordance with the disclosure in the aforementioned application, Serial No. 212,163.

Although the present invention is directed specifically to the production of electronically produced glide path line AB and runway line CD in Figure 1 on the elevation and azimuth displays, respectively, the present invention in' its broader aspects, Vwith the teachings incorporated herein, may be used for other purposes, where other .distinguishing lines on the displays are to be produced or certain control apparatus operated at predetermined spaced regions in the pattern and, as for example, as demonstrated, in the copending application of Raymond B. Tasker and Burton Cutler, two of the inventors herein, Serial No. 222,512, tiled April 23, 1951, the novel concepts incorporated herein may be used for producing limiting or clipping of the elevation or azimuth displays so that they appear as shown in Figure 1.

To demonstrate the manner in which this concept may be used in display limiting or clipping, specic circuitry is shown in Figure 2B which is claimed specically in the aforementioned application, Serial No. 222,512.

Brieiiy, such apparatus for producing pattern limiting or clipping serves to produce a so-called L trigger or blanking pulse instantaneously upon the deected cathode ray beam reaching the line LM or the lines KJH at the terminal designated as such in Figures 6 and 2C. Such L or blanking pulses may be used, as indicated in the moditied form in FigureV 8, to terminate, at critical variable times, the negative gating voltage initiated in the variable ywidth negative voltage generator stage 93 by the delayed synchronizing pulses supplied from the delay multivibrator stage 69. The output of the stage 93 is applied to the iirst anode SllCVof the cathode ray tube to produce blanking or darkening of the tube under the stated conditions, i. e., when the cathode ray beam reaches the line LM or the lines Klor JH inthe process of producing the displays.

y The .glide path AB, and' runway :line CDiajre formed by a series of cathode ray"i ntensifoying pulses whichY are produced when the cathode ray beam, swept `outwardly from the center O1 or O2, 4as thecase may be, reaches these positions. In other words, the time at which such intensifying pulses are applied' is determined by the angular position of the cathoderay sweep, i. e., 'the antenna beam angle voltage,.which is ameasure of the angular position of the corresponding antennabeam, and the time required for the cathode ray beam to move from the cen- -ter O1, O2, as the case maybe, tothe corresponding lines -AB and CD. This interrelations'bip between intensifying pulses, i. e., cursor pulses, timeand angular position of the particular cathode ray sweep is illustrated in Figures 9 and 10, which serve to correlate'the actual physical relationship of the`glide path or runwayline, as the case may be, to the electronically produced lines. It will be noted that electrical voltage (beam angle voltage) isVused to represent the angular orientation of specific points` on the actual glide path and runway lines, while time of electron beam travel serves as a measure of the distance to such specific point.

The method of approach to the solution of the problern may be explained as follows. If the aircraft, i. e., target, is assumed to be `flyingexactly along the desired glide path, its progress is indicated on the cathode ray tube-by a spot which traces out the glide path position. The location of this spot on-the tube face is determined by themagnitude of the expansion voltage applied to the modulator stage 75 (Figure 2C), and such spot is determined `also by the time required for the transmitted radar pulse to travel from the equipment adjacent the aircraft landing strip to the aircraft and back again to the equipment. For each value of angle Voltage, the time delay created mustV equal the time of pulse travel to and Yfrom the corresponding point onthe glide path. Thus,

for every spot on the glide path, there exists one and only one value of time delay, and elevation beam angle voltage or azimuth beam angle voltage, as the case may be.

Thus, Figure 3 lshows a three-dimensional geometrical representation of the desired safe aircraft glide path. The lineCD represents the center line of the runway and the `line AB is the glide path, intersecting the runway at the `touchdown point A at a vertical angle alpha. `tion of the radar antenna is at point R, and RB is a The locastraight line drawn from the antenna intersecting the .glide path at point B. Theta is the angle of elevation of `line RB, and phi is the azimuth angle measured betweenthe projection of RB Von the horizontal plane, and

.a .line parallel to the center line of the runway. Theta and phi, therefore, represent respectively Vertical and horizontal angles associated with the Vradar antennas when .they are directed at a point on the glide path. With the .radar in any fixed location with respect to the runway, and with a xed glide path angle, the distance RB is a .unique function of either theta or` phi.

Using this geometry and certain approximations, graphs or curves may oe drawn showing the `relationship between angle voltage and time delay. These curves, while not shown here, may be represented, as ,a close enough approximation, by the following expression:

il() a time delay dependent-*upon tangle voltage .in-.ascor- Vance withthe followingexpression: Y

where M is theslopefof the generated sawtooth wave, T0 is a constant time delay, V0 is the angle voltage corresponding either to the glide path angle or approach line anglein the azimuth display, and V is the corresponding azimuth or elevation angle Voltage. i

It will be further observed that the glide path and runway lines are determined essentiallyby two adjustments, i. e., Ythe corresponding straight lin'es are Vdetermined by two adjustable points on correspondingv lines.

The desired result obtained by the circuit described hereinafter may perhaps be understood better -by cornparing physical or space coordinates of miles and feet with corresponding electrical coordinates of vtime and voltage. Thus, in Figures 9 and 10, 02S, 02T, etc., represent either antenna beams in space orportions. of voltage sawteeth which in turn correspond to cathode ray tube beam sweeps. The circuit described hereinafter functions to produce a triggerV each vtime a sawtooth 02S, 02T, 02V, etc., intersects a voltage represented by the line CD, and thesertriggers are used to intensity modulate the cathode ray tube so that there is `produced electronically a line CD corresponding to the runway course line CD.

Similarly, Figures 11 and 12 show an elevation or right -of runway picture; here a similar transliguration is made from space to electrical coordinates. Thesawteeth voltlages intersect the inclined line AB which corresponds to the` glide path course line AB in Figure .11. The delay in time before the horizontal s'awtooth.O1-A intersects the line AB i-s a measure of the touchdown distance 01A in the elevation display. It is desired, for purposes of simplication of the equipment, to denne the glide path line AB in Figure l2 as aline which extends parallel to a reference line 01E passing through the origin O, tosimulate the condition in the azimuth display inFigure l0, wherein the runway course line CD extends'parallel to vthe reference line O2F passing `through-the origin ,02. These lines 02B and O1E1in Figures l0and llthus .rep- -resent reference voltages, the production and control of which form important aspects of the present invention.

More specifically, the presentation of a runwaycourse line in-the azimuth display, and the glide path course line inthe elevation display, is accomplished by ,modulating the CRT beam, moving from bottom to top, with a series of intensifying voltages (cursor pulses) which occur at increasingly shorter intervals (from the point of origin) on the azimuth display, and atfincreasingly longer intervals on the elevation display. The underlyingV principle of creatingthese cursor pulses involves generating a series of sawteeth (of relatively short duration), each one of which reaches the same relative voltage magnitude as .the applicable segment of antennabeamangle voltage. The sawteeth are made-to originate at timeswhich aresimultaneous `with theforigin of the time base sweep voltages. The pulses arezthen formed at-a constant voltage pointlon -the slope of'eachrsawtoothto simulatethecondition set iforth in Figure 10, using the parallel reference li-ne O2F or, in the elevation display,the parallel reference line 01E. Itshould be carefully noted that these Vlines OZFV application between increasing voltage and decreasing time is direct for establishing cursor pulses in the azimuth display, this relationship requires inversion in the elevation display with reference to Figure l2. Inversion is also required for the azimuth display in a right of runway installation. The fact that the ratio of antenna beam angle voltage to sawtooth voltage takes different directions for the azimuth and elevation displays, makes two separate modulation circuits necessary. The starting pointrfor the generation of sawteeth is determined by the required angle of azimuth or elevation display (corresponding to phi and theta in Figures 3, 9, l0, 11, 12) at which the cursor pulses are to start, and a voltage magnitude of zero is established for the sawtooth at this point. It should be carefully noted that the radial lines 02D and 01B which determine such angle correspond to a unique value of azimuth and elevation beam angle voltage, respectively.

In general, the sawteeth produced are amplilied and fed into a diode pickoi stage. Bias level of this stage determines the point on the slope of each sawtooth at which conduction takes place. This results in the formation of sawteeth having points of origin that diier from the original points by an amount determined by the bias level of the picko diode. The derivation of this bias level in elevation is the touchdown control, which varies the distance between the point of the time base sweep origin to the reference point of touchdown. The derivation of this bias level in azimuth is the runway control, which varies the distance between the point of the time base sweep origin to the reference point of touchdown on the runway centerline. The output from the picko diode is peaked and sent to a trigger forming circuit which produces the cursor pulses. The cursor pulses in the form of positivepulses are applied to the control grid 51A of the CRT51 for sweep intensification.

In general, the cursor pulses applied to the control grid 51A of the cathode ray tube, for purposes of producing the glide path course line AB and runway course line CD, are initiated, one per cathode ray beam sweep, in timed relationship with synchronizing pulses developed in the synchronizer 31 and applied to the circuitry shown in Figures 6 and 2B; however, it `should be carefully observed that this apparatus shown in these two figures functions to imparta predetermined unique time delay to each of such cursor pulses in accordance with the particular angular position of the cathodesweep, i. e., in accordance with the particular magnitude of the antenna beam angle voltage which, of course, serves as an indication of the position of the radiated antenna beam as well as determining such corresponding angular position of the cathode ray sweep. Y 4

Briefly, with reference to FigureY 6, the synchronizing pulses 123 are applied to a channel which includesthe variable delay multivibrator stage 100, the ditferentiating network 101, the variable length gate multivibrator'stag'e 104, the sweep generator stage 106, the amplifier stage 117, the diode pickoff or clipping lstage 109, the peaking circuit 114, and the iirst and second blocking oscillator stages 115 and 116, and the output of such stage v116 is applied to the cathode ray tube control grid 51A. The operation of this aforementioned channel is elfecte'd by the magnitude of either azimuth or elevation beam angle voltage, as the case may be, applied to the 'sweep-generator stage 106 in the formV indicated at 100A. It is remembered that these azimuth and elevation beam angle coupling voltages are developed and applied alternately to the sweep generator stage,106. The magnitude ofrthese voltages thus applied to stage 106 determines the position of the point B in the elevation display and the posi-v tion ofthe point D in the azimuth display. At angle voltrages greater than that corresponding to the sweep 02D, the sweep generator is rendered vfully operative ,to lVdeliver sawtooth Vvoltage variations in timed relationship with pulses 123,'such sawtooth variations then increasing- `dent with the pulse transmitted from the antennas.

trigger thus delayed is differentiated by the network comin magnitude with increase in angle voltage on the lead 136 to produce the series of sawtooth waves represented at 108.V Similarly, Vwith reference to the elevation/display (since inverted elevation angle voltage appears on the lead y136), the absolute value of the angle voltage appearing on the lead 136 is relatively small when the vsweepfoccupies the position 01B, and is relatively large when the'sweep occupies the position 01A. The threshold values lof angle voltage for determining the position of point D in Figure 10 and the position of the point B in Figure l2 is established by the position of the movable taps on the potentiometer resistances 122 and 121, respectively. These sawtooth waveforms 108, thus formed after this threshold value of angle voltage appears on the lead v136, are amplified in stage 117 and applied to the pickoff or clipping stage 109, where, during the azimuth display, such sawtooth waves have their initial portions clipped, i. e., rendered inetective as determined by the amount of positive Voltage appearing on the cathode of the tube 109. The voltage applied to such cathode during the azimuth display is a constant one and is represented by the distance a in Figure 10. Thereby such constant voltage applied to the cathode of the pickoit' tube establishes the distance of the line CD with respect to OZF. During the elevation display a constant voltage is applied to the cathode of tube 109, thereby establishing the distance of the line AB with respect to 01E as Yrepresented by the distance b.

Thus, recapitulating, the runway course line CD in the azimuth -display is determined by establishing first the `slope from the point D, using the control 122, and then vibrator tube 124 and initiates a positive gate on the anode of tube 12S. The length of the gate is determined by the Line adjust potentiometer resistance 127, which is normally set for a delay of 23 microseconds to be coin- The prising condenser 128 and resistance 129, 4and the resulting trailing edge triggers are applied to the normally conducting tube 133. The tube 134 aids in establishing the ymap length sweep gate (negative going) at the cathode of tube 133. The length of this developed gate is variable betweenv70 to 130 microseconds, which corresponds to 6 to 10 miles, by adjustment of the Az-El map length potentiometer resistance 130. This gate is then fed to the grid of the cursor sweep clamp tube 135 and also, for purposes described later, to the limiter sweep clamp tube 135A.

The stage 106, which includes the tube 135, includes also the condenser 107 having one of its terminals grounded and the other `one of its terminals connected to the anode of tube 135. The tube 135 normally, in its quiescent stage, conducts heavily since its control' grid is connected through resistances 135B and 135C to the positive terminal of source 167. It is noted further that the screen grid `of tube 135 is likewise connected to the sourceV 167 through resistance 135D. The anode of tube 135, however, is connected to the cath'odes of tubes 154 and 164 through lead 136. The anode of tube 135, and hence the condenser-107, are thus essentially at the same potential Yas the cathode of tube 135, namely, at 'ground potential. When the negative gating voltages are applied to the grid of tube 135, such grid is driven below the point of conduction and theico'ndenser 107 is thus al- 'lowed, during the duration of such gate, to be charged to'a maximum value determined by the particular magni- 13 tilde ofthe angle .vol'tage7`appearing'at that time on lead 13,67. Thus, when then-ow of space'current'through tube -135 `vis interruptedby such negative gating voltages, the angle voltage appearing on the lead 136 charges conden`ser107 through resistance V137.

It should be noted, however, that during certain por- Itions offthe cathode ray beam scanning cycle, the antenna Ibeam angle voltage is insuicient in 'magnitude to `conduct through the tube 154 or 164,.as theV case may be, andv in such casey there is of course no Charging of the joondenserf 107. "This condition corresponds in Figure to :the region on the display below thesweep 02D; and corresponds invFigure 12 to that portion of the` display Aabove thesweep 01B.

The manner in which antenna beam'angle voltage is lsupplied to thelead 136 is described in detail hereinafter, and for the present purposes itwill be assumed that there vis an` antenna beam angle voltagepresent on the lead :136, ,varying of course at a relatively slow rate, Vfor eiecting charging of the condenser 1 07 periodically at the -repetition rate of the. gating voltages applied 'to the grid .of tube 135. It should benoted that the sawteeth repre- 'sented as suchat 103 in.v Figure 6 .are caused to vary in amplitude in pr-oportiontol azimuth angle voltage in the azimuth display, and inversely proportional to elevation .angle voltage in the elevation display.

These voltage variations thus .appearing on the con- 'd'enserf107 areapplied to the amplifier stagej117 Ain the form of a `series of rising sawt-ooth voltages inthe azimuth tdisplays, and Va corresponding series of decreasing saw- `tooth voltages in the elevation displays, each starting from substantiallyzero voltage and rising to the voltage present ,on the lead, 136. In other Words, the voltage on lead 136, once apredetermined threshold value is applied to rfth'eanodes of tubes 154 and 164, is slightly higher at each cathoderaybeam sweep for azimuth (normal installation) .up?scan` and elevation down scan, and slightly lower -each sweep period for azimuth down scan and elevation "-up scan.

` Itshould be carefully noted that the duration of each .succeeding sawtooth voltage Wave developed in the stage :1.06, is'. equalbut, that the -changing amplitude results in y-sucessi'vely greater or successively lesser slopes. iThese sawto'oth-waves, after amplication in the stage y117, are applied to the anode of pickoff diode tube 109. The tube 109 conducts at an input level determined by the negative bias existing `on its cathode. The source of thls :cathode bias is isolated by the tube 138. This is accom- *pl'ished by 'connecting the cathodes of tubes 109 and 138 together and to the Aungrounded terminal of resistance `168, and by applying `suitable control voltages to the grld of tube 138. During the azimuth scan, the amount of vsuch control voltage is determined by the posrtlon of a @tap on potentiometer resistance 122, such tap being at a positive potential with respect to ground. The b1as i voltage on the cathode of tube 109 is alternately changed, depending upon whether or not the elevation or azimuth antenna is scanning through space in accordance with the energized condition of the Az-El relay 165, which serves i to alternately apply voltage from the adjustable tap on potentiometer 111 or 112 through the visolation stage 138 -tothe'cathode of tube 109. The sawtooth waves thus applied' through condenser `139 are subjected to the peaking circuit `114 which includes thetube 140, and then in succession to a first blocking oscillator stage 115 and then to .a second Vblocking oscillator stage 116.

In the peaker stage, which comprises the tubes 140 :and 141,' the degree of slope of each sawtooth 1s more sharply defined into a pulse waveform which 1s then applied lto the vgrid of the Vblocking oscillator bulrlng amplier tube 142. The time base follows the pattern of the varying sawtooth slopes, with the steeper sawtooth slopes representingshorter time intervals. For example, when the angle voltage rises as, a result of the azlrnuth touchdown point.

antenna sweeping left to right, the point of'zero mag:- nitude vsawtooth is determined by..thelse'tting of the Course yline angle potentiometer 122. At Vthe plate of the tube 109 the setting of the Distance to runway potentiometer 112 determines the steepness ofslope required before sawteeth may appear at the grid of the peaker circuit. It will be observed that the rst pulse to appear in` the oncoming series has the smallest slope, and as a consequence requires the greatest time to produce a trigger in the blocking voscillator circuit `115; whereas, the inal trigger in the series has thesteepest slope, and requires'the least time to form a trigger. 1n a normal left of runway installation display, the rs't trigger to appear in the blocking oscillator circuit 115 serves to plot the extreme end of the runway course line, i. e., the point D, and each resulting succeeding 'trigger establishes points on the line CD closer to the origin O2.

During up elevation scan periods the voltage appearing on the movable tap vof the End of glide path'resist ance 120, in the form of inverted'elevation angle voltage, is applied to the control grid of the bias forming tube 155. The anode of tube 155 is connected Vthrough resistance 155A to the control grid of tube 146, to thereby establish the bias on tube 146 in 'accordance with inverted elevation angle voltage duringthe elevation scanning period only, it being noted that the bias level established at this point during azimuth scan periods is a steady one, sufficientto Vmaintain tube'146 just under` the point of conduction until the rst pulse is transferred thereto from 'the cathode "of tubeV 143 through-'the coupling condenser 144. VDuring elevation scanning` periods,'however,V this inverted elevation angle voltage vappe'aringfon` the grid of tube 155, normally ina cutoff condition, causesthe tube 155 ltoriseto ajhighly conductive level whichv ,steadily changes of bias-andtriggers are in-opposing directions. The amplitude of the bias change, however, is variable ,bymeans ofthe End of glidepath potentiometer resistance, 111, which. allows the tube V146 to :be cut oi at a predetermined point near-the `ground line.

This, of course, determines the glide path end point as reproduced on the cathode ray tube screen. Thus, it is observed that the grid of the second blocking oscillator drivertube 146 is biased by inverted elevation angle voltage such that any triggers developed below an arbitrary angle voltage ila-elevation are not able to trigger yblocking oscillator 14S. rFlins the operator may stopV the glide pat-h at ground level (touchdown) if he so desires,

i. e., the position of thetap on resistance determines the termination of the glide path line precisely atpoint A. It is observed that this circuit does not affect the azimuth triggers, so that the runway line CD does not errninate at'the touchdown point but continues past the During the reverse scanning cycle of the azimuth and elevation antennas, angle voltage is also reversed,i. e., is of opposite slope. Since the progress of the time base and expansion deilection voltages is also VVreversed on the displays, the relationship of the course line cursor pulses remains fnred.

It is observed that in the upper left hand corner of Figure 2B a'switch 180 is provided, which, when closed, -serves to presentV a strobe on the display to indicate the origin of the sawteeth. Using this switch 130, the observer may adjust the resistance 127 to effect the proper delay in the multivibrator stage 100 withoutusing a synchroscope.

Recapitulating, during the azimuth scanning period, the 30-volt.relay gate developed at the start of the azimuth scanning period `and lasting during such ,period `energizes` relay tu-be 180, which draws currentV through relay windings 162 and 166. This causes closure of the -l-BOO-volt D.C. supply circuit 157 to the anodes of tubes 163 and 163A. The grid of tube 163 comprises a part of the input circuit of the azimuth cursor channel modulator circuit, and receives the antenna beam angle voltage (+2 volts to ,+52 volts) produced by the antenna coupling units. Since the action of relay 156, having control winding 162, cuts off the plate supply to this tube 163 during elevation scan periods, it reacts only to angle voltage coming from the azimuth antenna angle coupling unit. The cathode output of tube 163 goes through the lower closed contact of single pole single throw switch 151 into a voltage divider circuit comprising resistors 122A, 122B and Course line angle at origin control potentiometer 122. The tap on this potentiometer 122 serves to adjust the negative D.C. voltage level on lead 136 to thereby determine the angle of the runway course line at the point of origin, i. e., to establish the position of the line 02D in Figures 9 and l0. The position of the tap -on potentiometer 122 determines the angle between lines OZF and CD in Figure l; the tap is adjusted to make this angle zero degrees. During further upward azimuth scan, the cathode of tube 164, i. e., lead 136, delivers positive-going angle voltage to the anode of sweep clamp generator tube 135. Before proceeding further with the events occurring during the azimuth scan, the manner in which the elevation beam angle voltage is applied to the tube 135 during the elevation scan is rst described.

During periods of elevation antenna scanning, relay tube 180 becomes inactive, and relays 156 and 165 return to their normal position shown in Figure 2B. Under this condition, the source 157 is connected to supply space current to the tubes 152 and 152A. Tube 152 receives, at this time, elevation beam angle voltage on its grid and reproduces inverted elevation angle voltage on its plate circuit in the form indicated at 27B in Figure 5. The inverted elevation angle voltage is applied through the voltage divider circuit, comprising resistor 152B in series with Glide path angle at origin control potentiometer 121, to the plate of cathode follower 154 and the aforementioned lead 136. The position of the tap on potentiometer 121 determines the angle of the glide path AB by determining the point on the slope of the elevation beam angle voltage at which tube 154 starts conducting.

The functional operation of the circuit, for a complete scanning period, is as follows: Angle voltage, starting at 2 volts, and rising to 52 volts, is received from the azimuth antenna angle coupling unit and enters the circuit coincident with the reception of the +30-volt relay gate way installation). If the installation is on the right side r of the runway (from the pilots view), switch 151 is in right of runway position, and input to the plate of tube 164 is applied from the anode of tube 163A, the azimuth angle voltage in such case being inverted. Thus inverted azimuth beam angle voltage is applied to the cathode of tube 164, i. e., lead 136, and operation is similar to that described above for the formation of the elevation cursor pulses. The next quadrant of the complete scan cycle begins when the elevation antenna beam starts scanning upward and the rising elevation beam angle voltage is applied to the grid of tube 152 substantially coincident with lthe cessation of the map or Az-El relay gate.'V

Map limiting 0r map clipping As mentioned previously, the particular means used for pattern limiting or clipping may take diiferent forms, and the means shown for this purpose herein do not per se form a part of the present invention, it being described and claimed more fully in the aforementioned copending patent application of Raymond B.l Tasker and 16 Burton Cutler, Serial No. 222,512. As illustrative, however, of the manner in which the principles and concepts developed herein may be used for other purposes than merelyY for providing glide path and runway course lines, the following description relates to map limiting or clipping. Y

Briefly, instead of providing cursor pulses which are applied to the control grid of a tube to intensify the same, corresponding pulses, i. e., blanking or L pulses are produced to terminate or render invisible selected portions of cathode ray beam sweeps. Thus, these L or blanking pulses may, as indicated in Figure 8, be applied to a variable width negative gating voltage generator 93 to terminate at selected periods of time negative gating voltages 93A initiated in timed relationship with delayed synch pulses originating in the synchronizer unit 31. The resulting negative gating voltages'of variable length are then applied to the cathode of the cathode ray tube. In such case the cathode ray tube is adjusted so that the Video and range marks likewise applied to the cathode appear visibly on the cathode ray tube screen only during the duration of such negative gating voltages. Thus, if on a linear presentation the azimuth course line were moved up to the elevation level, and triggers were used to terminate unblanking gates, and if the elevation cursor were cut ot for all angles above that of zero degrees, one would have an Az-El sweep limiter.

Thus, pulses developed for the purpose of limiting the displays are developed in much the same type of circuit as used for developing the cursor pulses. The angle voltage modulator tubes 152A and 163A, used in elevation and in azimuth scanning, respectively, receive the corresponding antenna beam angle voltage generated in the angle coupling units. The output fromV these modulator tubes 152A, 163A is applied to cathode follower tubes 181, 182, respectively, through the limiting controls 184 and 185. The angle voltage appearing on the lead 186 Yconnected to the cathodes of tubes 181 and 182 is transferred to the limiter sweep clamping tube 135A. 'This modulator circuit is similar to the modulator circuit described above for generation of cursor pulses, with the exception that there is no need for inversion for right of runway installations. The end limit of the e1evation map is established by the position of the tap on the El-1 potentiometer 184, while the angle for end limit of the azimuth map is established by the Az-l potentiometer 185. The angle voltage above a predetermined threshold value is therefore applied to the anode of tube 135. The action of the sawtooth generating circuit, which includes tube 135A and condenser 135B is generally the same as described above for formation of cursor pulses. The sawteeth thus produced are applied to an amplifying circuitwhich includes the tubes 188, 189 and 190. This circuit employs degenerative feedback to improve the linearity which is controlled by the' Az-linearity potentiometer 192.A The output of this amplifier is applied to the anode of the diode pickoi tube 193, the cathode of which is biased in an amount determined by adjustment ofthe Az-2 potentiometer 194. Variation of the tap on resistance 194 establishes the position of the line LM in the vertical direction in the azimuth display inFigure l without changing appreciably its horizontal orientation.

The El-2 potentiometer 195 serves a like purpose in the elevation display, i. e. establishes the position of line JK with respect to the line OZL in the azimuth display without changing appreciably its angular orientation. The picked olf sawteeth are applied to the peaking amplifier tubes 196, 197. The output of this peaking circuit is applied to the grid of the tube 198 in the first blocking oscillator stage 199. The cathode output of the tube 200 is applied to the control grid of the modulator tube 201, to which is likewise applied inverted elevation angle voltage as produced at the plate of the inverter tube 202. It is observed that elevation angle voltage is applied to the control grid of tube 202 in an amount depending upon adjustment of the taps on the El base resistance 203. Adjustment of this resistance 203 establishes a limit on reproduction of the pulses at the anode of tube 201. Adjustment of resistance 203 establishes the orientation of line JH with respect to LM. Tube 201 thus acts in the same general manner as tube 146 in the cursor pulse circuit, i. e., tube 201 stops limiting at point J. The output appearing on the cathode of the nal blocking oscillator tube 205 appears at the terminal marked Blanking pulses and to the stage 93 in Figure 8, for the aforementioned purpose. These blanking pulses or so-called L triggers, which dornot apepar because of the biasing action of resistance 203, are replaced with triggers formed by the termination of the map length multivibrator gate from the cathode of tube 133, which gates are differentiated by means of condenser 206 and resistance 207. All of these L or blanking triggers reach an amplitude of approximately |-30 volts, have a duration of approximately one microsecond, and are delayed from 8 to 124 microseconds, as measured from the time of the radiated pulse, i. e., from point O1 or O2, as the case may be.

It is observed that the second blocking oscillator driving grid in the pattern limiting circuit is modulated with elevation angle voltage, but in the opposite manner as in the cursor circuit, so that all triggers in the pattern limiting circuit above the horizontal may be gated 01T.

While the particular embodiments of the present invention have been shown and described, it will be obvious to-those skilled in the art that changes and modifications may be made without departing from this invention in its broader aspects and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.

We claim:

1. In a system of the character described, energy transmitting means periodically triggered at a relatively high rate to produce an antenna beam, means for-scanning said antenna beam in space, means deriving an angle voltage, the instantaneous magnitude of Awhich is representative of the position of the antenna beam, a cathode ray tube having cathode beam detlecting means, means operated synchronously with said transmitting means for energizing said beam deflecting means to produce cathode beam sweeps, said cathode ray tube having an intensity controlling electrode, means producing a series of sawtooth waves, each of substantially the same time duration and appearing in timed relationship with operation of said transmitting means with the intensity of each of said sawtooth waves being representative of the instantaneous magnitude of said angle voltage, means picking off the peaks of said series of sawtooth waves and producing a corresponding series of voltage variations each starting at different times with respect to energization of said beam deflecting means, means peaking the last men)- tioned voltage variations and applying the resulting peaked waves to said intensity 4controlling electrode.

2. In a system of the character described, an azimuth antenna, an elevation antenna, energy transmitting means periodically triggered at a relatively high rate, means alternately coupling said transmitting means to said azimuth antenna and said elevation antenna at a relatively low` rate to produce alternately a plurality of azimuth antenna beams and a plurality of elevation antenna beams, means operating synchronously with said coupling means for scanning each of said antenna beams in space, means deriving a corresponding azimuth angle voltage and an elevation angle voltage, the instantaneous magnitude of each of which is representative respectively of the position of the azimuth and elevation beams, a cathode ray tube having cathode beam deecting means, two position beam centering means alternately effective to move the cathode beam to different adjusted center positions, means operated synchronously with said transmitting means for energizing said beam deecting means to produce cathode beam sweeps, means operated synchronously with said coupling means to change from one of said centering means to the other centering means and to alternately and synchronously apply said azimuth and elevation angle voltage to one of said beam deilecting means, to thereby obtain alternate azimuth and elevation displays of the space scanned by said azimuth and elevation antenna beams, said cathode ray tube having an intensity controlling electrode, means lfor generating a series of sawtooth waves, each of substantially the same time duration and appearing in timed relationship with operation of said transmitting means, said last mentioned sawtooth generating means including means for alternately applying said azimuth and elevation angle voltages thereto and for producing sawtooth waves therein varying in amplitude in accordance with the intensity of either the azimuth or elevation angle voltage, as the case may be, means picking off the peaks of said sawtooth waves of variable amplitude and producing a corresponding series of time displaced waves, means peaking each of said time displaced waves and applying the resulting peaked waves to said intensity controlling electrode.

3. Ina system of the character described, a cathode ray tube, means producing an antenna beam which consists of a series of pulses occurring at a relatively high rate, means for scanning said antenna beam at a relatively low rate, means deriving a beam angle voltage the magnitude of which is representative of the angular position of the antenna beam, means periodically producing a cathode beam sweep in timed relationship with operation of said antenna beam producingimeans to produce a two dimensional display in which the sweeps start at a common origin, means including said beam angle voltage deriving means for producing a ASeries of time spaced peaked voltages which start at different times with respect to operation of said sweep producing means, means applying said peaked waves to an intensity control electrode of said cathode ray tube to produce a visible trace on said tube in accordance with said peaked waves, and further including independent means for adjusting the inclination and distance from the origin of said trace in said display.

4. In a system of the character described, a cathode ray tube, means producing an antenna beam which consists of a series of pulses occurring at a relatively high rate, means for scanning said antenna beam at a relatively low rate, means deriving a beam angle voltage the magnitude of which is representative of the angular `position of the antenna beam, means periodically producing a cathode beam sweep in timed relationship with operation of said antenna beam producing means, means including said beam angle voltage deriving .means for producing a series of sawtooth waves, each of substantially the same time duration and appearing in timed relationship with operation of said antenna beam producing means with each of said sawtooth waves varying in arnplitude in accordance with the angular position of said antenna beam and with said series occurring at said relatively low rate, means picking oi-the peaks of said sawtooth waves in each series and producing a corresponding series of waves displaced in time with respect -to the time of operation of said sweep producing means,

means peaking said series of waves toV produce corresponding peaked waves, and means applying said peaked waves to an intensity control electrode of said cathode ray tube.

5. In an arrangement of the character described, ra

'cathode ray tube, cathode beam sweep producing means,

cathode beam intensifying means, antenna means, synchronizing means, means for deriving pulsed energy in accordance with triggers produced by said synchronizing means, means transferring said pulsed energy to said antenna means to produce a pulsed energy beam, means `scanning said pulsed energy beam through space, means de'r'iving"` an angle vvoltage representative of the angular position of the pulsed energy beam, means energizing 'said cathode beam sweep producing means periodically in 'synchronism with development of said triggers, means modulating said sweep producing means with said angle voltage 'to produce a series of displaced cathode beam sweeps' each of substantially the same time duration, condenser rneans, means periodically charging said vcondenser with said angle voltage in synchronism with the appearance of said triggers, and developing a series of variable intensityv voltage waves varying in time, pickoi means for' deriving voltage variations displaced in time with respect to operation of said sweep producing means and in accordance with the intensity of said voltage waves, peaking means coupled to said pickoff means for developing corresponding peaked waves, and means coupling said peaking means to said cathode beam intensity control means.

6. In a system 'of the character described, a cathode fray tube, antenna means, means periodically operative for transferring energy to said antenna means to produce anantenna beam, means producing cathode beam sweeps in said tube in timed relationship with operation of said energy transferring means, means for scanning said antenna beam through space at a relatively low rate, means producing an angle voltage representative of the Vposition of said antenna beam in space, means generating a series Iof variable intensity sawtooth waves, each of substantially the same time duration and appearing in timed relationship with operation of said energy transferring means, the intensity of each of said sawtooth waves being representative of the instantaneous angle voltage, picko means for picking off the peaks of said series of sawtooth waves Vand producing a corresponding series of peaked waves spaced in time with respect to operation of said cathode beam sweep producing means, and means applying said peaked waves to an intensity control electrode of said cathode ray tube.

7. 'In a system of the character described, cathode ray Vtube indicating means, beam deflecting means operative to move the cathode beam to produce a sweep, cathode beam intensifying means, said beam derecting means controlling the transverse distance travelled 'by the beam `and also 'said beam intensifying means to produce visible Aindications on successive sweeps at different distances Vfrom the origin of the sweeps, and means for adjusting the position of said indications.

8. In a system of the character described, means producing an 'antenna beam and scanning the same through space, cathode ray tube indicating means, beam deecting means operative to move the cathode beam to produce succesive sweeps and 'produce a two dimensional display, cathode beam intensifying means, means deriving an antenna beam angle voltage which is representative of the position of said antenna beam in space, means 'modulating said beam deecting means with Said angle voltage tofproduce lateral displacement of said sweeps, and means 'controlled by said angle voltage for operating said beam intensifying means at diiferent times during and after initiation of successive sweeps to thereby change the visible character of intermediate portions of each of the successive sweeps and produce a line in said display, and means for adjusting the position of said 'line in said display independently as to its inclination and position.

9. vIn a system of the character described, means producing an antenna beam and scanning the same through space, a sweep generator including a condenser, means deriving a source of beam angle voltage varying in amplitude at a relatively low rate in accordance with the position of said antenna beam in space and coupled to said condenser for charging the same, a source of triggering pulses coupled to said sweep generator for successively altering the'charged condition of said condenser at '20 condenser for deriving therefrom a plurality of voltage waves, each starting at. different times with respect to appearance of said triggering pulses.

-10. In a system of the character described, a sweep generator including acondenser, a source of beam angle voltage, the amplitude of which varies in accordance with the position of an antenna beam, means coupling said source of beam angle voltage to said condenser for charging the same at a relatively low rate, a source of triggering pulses coupled to said condenser for periodically discharging the same at Aa relatively high rate, said sweep generator including means for developing a series of sawtooth waves, each of substantially the same time duration and with each sawtooth wave initiated at the same time in relationship to the appearance of said triggering pulses, but, said sawtooth waves having amplitudes varying in accordance with the instantaneous magnitude of beam angle voltage, sawtooth voltage wave pickoff means coupled to said condenser and producing from said voltage waves a corresponding series of clipped voltage waves each starting at different times with respect to the appearance of said triggering pulses. 1l. The arrangement set forth in claim l0 in which adjustable means are provided for adjusting the magnitude of beam angle voltage applied to said condenser.'

l2. The arrangement set forth in claim l0 in which adjustable means are incorporated for adjusting the level of operation of said sawtooth voltage wave pickoit' means.

13. The arrangement set forth in claim 10 in which adjustable Vmeans are provided for adjusting the magnitude of the beam angle voltageapplied to said condenser, and adjustable means are incorporated for adjusting the level of operation of said sawtooth Voltage wave pickotf means.

14. The arrangement set forth in claim 10 in which a utilizationchannel is coupled to said pickoff means to pass said clipped voltage waves, and means coupled to "said source of beam angle voltage for rendering said channel inoperative in accordance with the predetermined magnitude of said beam angle voltage.

I15. The arrangement set forth in claim l0 including 'also a cathode ray tube, cathode beam deflecting means operative to produce la cathode beam sweep, means modulating said beam deflecting means with beam angle 'voltage to produce lateral movement of successive sweeps, and means coupling said clipped voltage Waves to an intensity control electrode of said cathode ray tube. V16. The arrangement set forth in claim l0 including Yalso a cathode ray tube, cathode beam deecting means operative to produce a cathode beam sweep, means modulating said beam deecting means with beam angle :voltage to produce lateral movement of successive sweeps,'means coupling said clipped voltage waves to an intensity control electrode of said cathode ray tube, the 'beam angle voltage applied to said cathode beam deflecting-means and to said condenser varying in the same direction.

-17. The arrangement set forth in claim 10 including also a cathode Vray tube, cathode beam detlecting means operative yto produce a cathode beam sweep, means modulating said :beam deecting means with beam angle voltage to produce ylateral movement of successive sweeps, means coupling said clipped voltage Waves to an Yintensity control electrode of said cathode ray tube, the

ulating said beam .deecting .means with beam angle voltage to V-produce ilateral movement of successive sweeps, means coupling said clipped voltage Waves to an intensity control electrode of said cathode ray tube, the

beam. angle voltage applied to said cathode beam` deecting means and to-said condenser varying in opposite directions, said beam angle voltage'varying in the same direction as that beam angle voltage` applied Vto the condenser is coupled to said voltage coupling means to render the same inoperative upon attainment of a predetermined beam angle voltage.

19. In a system of the character described, an azimuth antenna, an elevation antenna, energy transmitting means periodically triggered at a relatively high rate, means alternately coupling said transmitting means to said azimuth antenna and said elevation antenna at a relatively low rate to produce alternately a plurality of azimuth antenna beams and a plurality of elevation antenna beams, means operating synchronously with said coupling means for scanning each of said antenna beams in space, means deriving a corresponding azimuth angle voltage and an elevation angle voltage, the instantaneous magnitude of each of which is representative respectively of the position of the azimuth and elevation beams, a cathode ray tube'having cathode beam deflecting means, two position beam centering means alternately eiective to move the cathode beam to different adjusted center positions, means operated synchronously with said transmitting means for energizing said beam deflecting means to produce cathode beam sweeps, means operated synchronously with said coupling means to change from one of said centering means to the other centering means and to alternately and synchronously apply said azimuth and elevation angle voltage to one of said beam deecting means, to thereby obtain alternate azimuth and elevation displays of the space scanned respectively by said azimuth and elevation antenna beams, said cathode ray tube having an intensity control electrode, means for generating a series of time spaced cathode beam intensifying pulses, said series being generated in timed relationship with operation of said transmitting means, said last mentioned generating means being responsive to the amplitude of elevation and azimuth angle voltages and including means for alternately applying said azimuth and elevation angle voltages thereto and for spacing said pulses at different times with respect to time of operation of said transmitting means in accordance either with the amplitude of the azimuth orelevation angle voltage, as the case may be, and means coupling said intensifying pulse generating means to said intensity controlling electrode.

20. In an arrangement of the character described for producing predetermined aircraft glide paths or runway course lines, energy transmitting means periodically triggered at a relatively high rate to produce an antenna beam, means for scanning said antenna beam in space, means deriving an angle voltage, the instantaneous magnitude of which is representative of the position of the antenna beam, a cathode ray tube having cathode beam deecting means, means operated synchronously with said transmitting means for energizing said beam deecting means to produce cathode beam sweeps, each of substantially the same time duration, means modulating said sweep in accordance with the amplitude of said angle voltage, said cathode ray tube having an intensity controlling electrode, means including said intensity controlling electrode and responsive to the amplitude of said angle voltage for changing the visible character of a portion of each one of said cathode beam sweeps to form a visible trace, said portion of each of said 4sweeps being spaced variable distances from the origin of the sweeps in accordance with the following expression:

where a, b and c are mathematical constants, V is equal to the magnitude of said angle voltage, and T represents the time it requires the corresponding sweep to travel from the origin of the sweeps to said portion of the ducing an antenna beam and scanning the same through` space, visual indicating means, said visual indicatingv means including means for developing radial sweeps and for producing an expanded representation of the space scanned by said antenna beam with said radial sweeps, and means synchronously operated with movement of said antenna beam for producing a trace on said visualV indicating means which is inclined with respect to substantially all of said radial sweeps with different points.

on said trace representing diierent range distances in said space, said trace being representative of. a predeterminedv ght path of an object in said space, and independently adjustable means for adjustingV the inclination of said trace and its distance from the origin of said radial sweeps.

22. In a system of the character described, means producing an antenna beam and scanning the same through space, means deriving an electrical characteristic, the magnitude of which varies in accordance with the angular position of said antenna beam in space, visual indicating means, said visual indicating means including means controlled by said electrical characteristic for producing radial sweeps and for producing an expanded visual representation of said space on said visual indicating means with said radial sweeps, and means controlled by said electrical characteristic for producing a trace on said visual indicating means inclined with respect to substantially all of said radial sweeps with different points on said trace representing different range distances in said space, said trace being representative of a predeterminated ight path of an object in said space, and means for adjusting the inclination of said trace.

23. In a system of the character described, means producing an antenna beam and scanning the same through space at a relatively low rate, said antenna beam producing means including a source of triggering voltage pulses occurring at a relatively high rate, means deriving an electrical characteristic, the magnitude of which varies in accordance with the angular position of said antenna beam in space, visual indicating means sensitive to said electrical characteristic for producing radial sweeps and for producing an expanded visual representation of said space with said radial sweeps, and means sensitive to both said electrical characteristic and said triggering voltage pulses for producing a trace on said visual indicating means inclined with respect to substantially all of said radial sweeps with diierent points on said trace representing diierent range distances in said space, said trace being representative of the Hight path of an object in said space, and means for adjusting a terminal point of said trace with respect to its distance from the origin of said radial sweeps.

24. In a system of the character described, means producing an antenna beam and scanning the same through space, visual indicating means, said visual indicating means using polar sweeps of a cathode ray beam and producing an expanded representation of said space, and means producing a visual trace on said visual indicating means inclined with respect to substantially all of said sweeps with different points on said trace representing dierent range distances in said space, said trace being representative of a predetermined ight path of an object in said space, and means for independently adjusting the inclination of said trace.

25. In a system of the character described, means producing an antenna beam and scanning the same through space, visual indicating means producing a visual representation of said space, said visual indicating means including a cathode ray tube with means for producing polar sweeps, and means operated synchronously with movement of said antenna beam through said space for producing a trace inclined with respect to substantially all of said sweeps with different points on said trace representing diierent range distances in said space, said trace representing a predetermined flight path of an object in said space, means for adjusting the inclination of said trace, and means for adjusting a terminal point on said trace with respect to its distance from the origin of said polar sweeps.

26. In a system of the characterdescribed, cathode ray tube indicating means, beam deecting means operative to move the cathode beam to produce a sweep, cathode beam intensifying means, and means operated at a different time after the initiation of each successive sweep andrcontrolling the operation of said beam intensifying means to produce visible indications on successive sweeps at diierent distances from the origin of the sweeps to produce a trace, means for adjusting the inclination of said trace, and means for adjusting the position of a terminal point of said trace.

CFI

27. In a system of the character described, means producing an antenna beam andV scanning the same'throuvgh' space, visual indicating means, said visual indicating means including means for developing radial sweeps, and means synchronously operated with movement of said antenna beam for producing a trace on said visual indicating means which is inclined withl respect to substantially all of said radial sweeps, said trace being representative of a predetermined ight path of an object in said space means for adjusting the inclination of said trace, and means for adjusting the position of a terminal point of said trace.

References Cited in the file of this patent UNITED STATES PATENTS 2,459,481 Woli et al. Jan. 18, 1949 2,512,703 Wilkerson June 27, 1950 2,555,101 Alvarez et al May 20, 1951 2,585,855 Sherwin et al. Feb. 12, 1952 2,616,078 Fyler Oct. 28, 1952 

